研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙物理学研究系 助教
- 学位
- 博士(理学)(2002年3月 東京大学理学系研究科物理学専攻)
- J-GLOBAL ID
- 202001017082346100
- researchmap会員ID
- R000012159
経歴
10-
2019年4月 - 現在
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2018年4月 - 2019年3月
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2017年4月 - 2018年3月
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2016年4月 - 2017年3月
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2011年4月 - 2016年3月
学歴
2-
1999年4月 - 2002年3月
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1997年4月 - 1999年3月
受賞
2論文
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The Astrophysical Journal 2023年8月1日 査読有り筆頭著者
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The Astrophysical Journal 2023年7月1日
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Probing Dynamics and Thermal Properties Inside Molecular Tori with CO Rovibrational Absorption LinesThe Astrophysical Journal 934(1) 25-25 2022年7月1日 査読有りAbstract A recent hydrodynamic model, the radiation-driven fountain model (Wada et al. 2016), presented a dynamical picture that active galactic nuclei (AGNs) tori sustain their geometrical thickness by gas circulation around AGNs, and previous papers have confirmed that this picture is consistent with multiwavelength observations of nearby Seyfert galaxies. Recent near-infrared observations implied that CO rovibrational absorption lines (ΔJ = ± 1, v = 0 − 1, λ ∼ 4.7 μm) could probe the physical properties of the inside tori. However, the origin of the CO absorption lines has been under debate. In this paper, we investigate the origin of the absorption lines and conditions for detecting them by performing line radiative transfer calculations based on the radiation-driven fountain model. We find that CO rovibrational absorption lines are detected at inclination angles θobs = 50°–80°. At the inclination angle θobs = 77°, we observe multi-velocity components: inflow (vLOS = 30 km s−1), systemic (vLOS = 0 km s−1), and outflows (vLOS = −75, − 95, and −105 km s−1). The inflow and outflow components (vLOS = 30 and −95 km s−1) are collisionally excited at the excitation temperatures of 186 and 380 K up to J = 12 and 4, respectively. The inflow and outflow components originate from the accreting gas on the equatorial plane at 1.5 pc from the AGN center and the outflowing gas driven by AGN radiation pressure at 1.0 pc, respectively. These results suggest that CO rovibrational absorption lines can provide us with the velocities and kinetic temperatures of the inflow and outflow in the inner few parsec region of AGN tori, and the observations can probe the gas circulation inside the tori.
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The Astrophysical Journal 928(2) 184-184 2022年4月1日 査読有りAbstract The ultraluminous infrared galaxy IRAS 17208−0014 is a late-stage merger that hosts a buried active galactic nucleus (AGN). To investigate its nuclear structure, we performed high-spatial-resolution ( ∼ 0.″04 ∼ 32 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 9 (∼450 μm or ∼660 GHz), along with near-infrared AKARI spectroscopy in 2.5–5.0 μm. The Band 9 dust continuum peaks at the AGN location, and toward this position CO(J = 6 − 5) and CS(J = 14 − 13) are detected in absorption. Comparison with nonlocal thermal equilibrium calculations indicates that, within the central beam (r ∼ 20 pc), there exists a concentrated component that is dense (107 cm−3) and warm (>200 K) and has a large column density (${N}_{ { {\rm{H } } }_{2 } }\gt {10}^{23}\,{\mathrm{cm } }^{-2}$). The AKARI spectrum shows deep and broad CO rovibrational absorption at 4.67 μm. Its band profile is well reproduced with a similarly dense and large column but hotter (∼1000 K) gas. The region observed through absorption in the near-infrared is highly likely in the nuclear direction, as in the submillimeter, but with a narrower beam including a region closer to the nucleus. The central component is considered to possess a hot structure where vibrationally excited HCN emission originates. The most plausible heating source for the gas is X-rays from the AGN. The AKARI spectrum does not show other AGN signs in 2.5–4 μm, but this absence may be usual for AGNs buried in a hot mid-infrared core. Further, based on our ALMA observations, we relate the various nuclear structures of IRAS 17208−0014 that have been proposed in the literature.
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Monthly Notices of the Royal Astronomical Society 512(4) 5995-6006 2022年3月25日 査読有りABSTRACT The far-infrared counterpart of hotspot D, the terminal hotspot of the eastern jet hosted by the radio galaxy Cygnus A, is detected with Herschel Aperture photometry of the source performed in 5 photometric bands covering the wavelength range of 70–350 $\mu$m. After removing the contamination from another nearby hotspot, E, the far-infrared intensity of hotspot D is derived as 83 ± 13 and 269 ± 66 mJy at 160 and 350 $\mu$m, respectively. Since the far-infrared spectrum of the object smoothly connects to the radio one, the far-infrared emission is attributed to the synchrotron radiation from the radio-emitting electron population. The radio-to-near-infrared spectrum is confirmed to exhibit a far-infrared break feature at the frequency of $\nu _\mathrm{br}=2.0^{+1.2}_{-0.8} \times 10^{12}$ Hz. The change in energy index at the break (Δα = 0.5) is interpreted as the impact of radiative cooling on an electron distribution sustained by continuous injection from diffusive shock acceleration. By ascribing the derived break to this cooling break, the magnetic field, B, in the hotspot is determined as a function of its radius, R within a uniform one-zone model combined with the strong relativistic shock condition. An independent B–R constraint is obtained by assuming the X-ray spectrum is wholly due to synchrotron self-Compton emission. By combining these conditions, the two parameters are tightly determined as B = 120–150 μG and R = 1.3–1.6 kpc. A further investigation into the two conditions indicates the observed X-ray flux is highly dominated by the synchrotron self-Compton emission.
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The Astrophysical Journal 922(2) 272-272 2021年12月1日 査読有り<title>Abstract</title> We conducted systematic observations of the H <sc>i</sc> Br<italic>α</italic> (4.05 <italic>μ</italic>m) and Br<italic>β</italic> (2.63 <italic>μ</italic>m) lines in 52 nearby (<italic>z</italic> < 0.3) ultraluminous infrared galaxies (ULIRGs) with AKARI. Among 33 ULIRGs wherein the lines are detected, 3 galaxies show anomalous Br<italic>β</italic>/Br<italic>α</italic> line ratios (∼1.0), which are significantly higher than those for case B (0.565). Our observations also show that ULIRGs have a tendency to exhibit higher Br<italic>β</italic>/Br<italic>α</italic> line ratios than those observed in Galactic H <sc>ii</sc> regions. The high Br<italic>β</italic>/Br<italic>α</italic> line ratios cannot be explained by a combination of dust extinction and case B since dust extinction reduces the ratio. We explore possible causes for the high Br<italic>β</italic>/Br<italic>α</italic> line ratios and show that the observed ratios can be explained by a combination of an optically thick Br<italic>α</italic> line and an optically thin Br<italic>β</italic> line. We simulated the H <sc>ii</sc> regions in ULIRGs with the Cloudy code, and our results show that the high Br<italic>β</italic>/Br<italic>α</italic> line ratios can be explained by high-density conditions, wherein the Br<italic>α</italic> line becomes optically thick. To achieve a column density large enough to make the Br<italic>α</italic> line optically thick within a single H <sc>ii</sc> region, the gas density must be as high as <italic>n</italic> ∼ 108 cm−3. We therefore propose an ensemble of H <sc>ii</sc> regions, in each of which the Br<italic>α</italic> line is optically thick, to explain the high Br<italic>β</italic>/Br<italic>α</italic> line ratio.
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The Astrophysical Journal 921(2) 141-141 2021年11月1日 査読有りUnderstanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines (Delta nu = 0 -> 1, Delta J= +/- 1) at lambda similar to 4.67 mu m observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy (R similar to 10,000) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately similar to-160 km s(-1), but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately similar to+100 km s(-1), which were attributed to the torus. The ratios of the velocity dispersions of each component led to those of the rotating radii around the black hole of R-rot,R-a: R-rot,R-b: R-rot,R-c approximate to 1: 5: 17, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with sigma(V) proportional to R-rot(-0.5) is assumed. Based on the kinetic temperature of components (a) and (b) of similar to 720 and similar to 25 K, respectively, estimated from the level population, the temperature gradient is T-kin proportional to R-rot(-)2.1. Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient.
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The Astrophysical Journal 899(1) 17-17 2020年8月7日 査読有り筆頭著者
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The Astrophysical Journal 884(2) 132-132 2019年10月18日 査読有りWe investigate the precise location of the radio core in the nearby blazar Mrk 501 for the first time during its X-ray and TeV gamma-ray active state in 2012 by revisiting from the perspective of astrometry the six-epoch observations with the Very Long Baseline Array at 43 GHz reported by Koyama et al. We find that the position of the radio core seen at 43 GHz remained stable during our observations from 2012 to 2013 February within 42 mu as in the southeast jet direction and 56 mu as along the northeast jet direction. This implies that the location of the 43 GHz radio-emitting core was limited within the deprojected scale of 4.6 x 10(3) Schwarzschild radii (R-s) during the high-energy active state. This result is a contrast to another case of the astrometric observation of the famous nearby TeV blazar Mrk 421, which showed a clear radio core position change soon after the large X-ray flare in 2011, reported by Niinuma et al. We compare the two cases and discuss possible origins of the different results of the radio core astrometry in the high-energy active states between the nearby blazars. Based on the internal shock model for blazars, the Lorentz factors of the ejecta explaining the stability of the radio core in Mrk 501 are expected to be a few times smaller than those for the wandering core in Mrk 421.
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Publications of the Astronomical Society of Japan 71(2) 2019年4月1日 査読有りWe present a systematic study of the 3.0 mu m H2O ice and the 3.4 mu m aliphatic carbon absorption features toward 48 local ultraluminous infrared galaxies (ULIRGs) using spectra obtained by the AKARI Infrared Camera to investigate the UV environment in their star-forming regions. All the ULIRGs in our sample exhibit a ratio of optical depth of H2O ice to silicate dust (tau(3.0)/tau(9.7)) that is lower than that in the Taurus dark cloud. This implies that ULIRGs cannot be described as an ensemble of low-mass star-forming regions and that a significant amount of high-mass star-forming regions contribute to star-forming clouds in local ULIRGs. The results also show that the ratios of optical depth of aliphatic carbon to silicate dust, tau(3.4)/tau(9.7), exhibit diverse values. We investigate two effects that can affect this ratio: the geometric temperature gradient (which increases the ratio) and the intense UV environment (which decreases it). The geometric temperature gradient is typically considered as a sign of active galactic nuclei (AGN). ULIRGs with AGN signs (optical classification, near-infrared color, and a polycyclic aromatic hydrocarbon emission strength of 3.3 mu m) indeed tend to exhibit a large tau(3.4)/tau(9.7) ratio. However, we find that the presence of buried AGN is not the only cause of the geometric temperature gradient, because the enhancement of the ratio is also evident in pure starburst-like ULIRGs without these AGN signs. Regarding the intense UV environment in star-forming regions, the correlation between the aliphatic carbon ratio and the ratio of the [C II] 158 mu m line luminosity to the far-infrared luminosity (L-[C II]/L-FIR), which represents the UV environment in photodissociation regions, implies that the intense UV environment causes the decrease of the aliphatic carbon ratio. We find that an intense UV environment (G/n(H) > 3) in star-forming regions is needed for the aliphatic carbon ratio to be suppressed.
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 17(4) 477-482 2019年
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The Astrophysical Journal Supplement Series 238(2) 32-32 2018年10月15日 査読有りWe present the third MAXI/GSC catalog in the high Galactic latitude sky (vertical bar b vertical bar > 10 degrees) based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic latitude sky (vertical bar b vertical bar < 10 degrees) (Hori et al. 2018). We compile 682 sources detected at significances of s(D,4-10 keV) >= 6.5 in the 4-10 keV band. A two-dimensional image fit based on the Poisson likelihood algorithm (C-statistics) is adopted for the detections and constraints on their fluxes and positions. The 4-10 keV sensitivity reaches approximate to 0.48 mCrab, or approximate to 5.9 x 10(-12) erg cm(-2) s(-1), over half of the survey area. Compared with the 37-month Hiroi et al. (2013) catalog, which adopted a threshold of s(D,4-10) (keV) >= 7, the source number increases by a factor of similar to 1.4. The fluxes in the 3-4 keV and 10-20 keV bands are further estimated, and hardness ratios (HRs) are calculated using the 3-4 keV, 4-10 keV, 3-10 keV, and 10-20 keV band fluxes. We also make the 4-10 keV light curves in 1-year bins for all the sources and characterize their variabilities with an index based on a likelihood function and the excess variance. Possible counterparts are found from five major X-ray survey catalogs by Swift, Uhuru, RXTE, XMM-Newton, and ROSAT, as well as an X-ray galaxy cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, 1-year bin light curves, variability indices, and counterpart candidates.
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Journal of Astronomical Telescopes, Instruments, and Systems 4(04) 1-1 2018年10月4日 査読有り© 2018 The Authors. Toward an era of x-ray astronomy, next-generation x-ray optics are indispensable. To meet a demand for telescopes lighter than the foil optics but with a better angular resolution <1 arcmin, we are developing micropore x-ray optics based on micromaching technologies. Using sidewalls of micropores through a thin silicon wafer, this type can be the lightest x-ray telescope ever achieved. Two Japanese missions, ORBIS and GEO-X, will carry this telescope. ORBIS is a small x-ray astronomy mission to monitor supermassive blackholes, while GEO-X is a small exploration mission of the Earth's magnetosphere. Both missions need an ultralightweight (<1 kg) telescope with moderately good angular resolution (<10 arcmin) at an extremely short focal length (<30 cm). We plan to demonstrate this type of telescope in these two missions around 2020.
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Publications of the Astronomical Society of Australia 35 2018年8月 査読有り<title>Abstract</title>Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity. SPICA takes the next step in infrared observational capability by combining a large 2.5-meter diameter telescope, cooled to below 8 K, with instruments employing ultra-sensitive detectors. A combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With mechanical coolers the mission lifetime is not limited by the supply of cryogen. With the combination of low telescope background and instruments with state-of-the-art detectors SPICA provides a huge advance on the capabilities of previous missions. SPICA instruments offer spectral resolving power ranging from <italic>R</italic> ~50 through 11 000 in the 17–230 μm domain and <italic>R</italic> ~28.000 spectroscopy between 12 and 18 μm. SPICA will provide efficient 30–37 μm broad band mapping, and small field spectroscopic and polarimetric imaging at 100, 200 and 350 μm. SPICA will provide infrared spectroscopy with an unprecedented sensitivity of ~5 × 10−20 W m−2 (5σ/1 h)—over two orders of magnitude improvement over what earlier missions. This exceptional performance leap, will open entirely new domains in infrared astronomy; galaxy evolution and metal production over cosmic time, dust formation and evolution from very early epochs onwards, the formation history of planetary systems.
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The Astrophysical Journal Supplement Series 235(1) 7-7 2018年2月26日 査読有り
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 882 138-147 2018年2月 査読有り
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The Astrophysical Journal 852(2) 83-83 2018年1月9日 査読有りWe performed a systematic analysis of the 4.67 mu m CO ro-vibrational absorption band toward nearby active galactic nuclei (AGNs) and analyzed the absorption profiles of 10 nearby galaxies collected from the AKARI and Spitzer spectroscopic observations that show the CO absorption feature by fitting a plane-parallel local thermal equilibrium gas model. We found that CO gas is warm (200-500 K) and has a large column density (N-H greater than or similar to 10(23) cm(-2)). The heating of the gas is not explicable by either UV heating or shock heating because these processes cannot represent the large column densities of the warm gas. Instead, X-ray photons from the nuclei, which can produce large columns of warm gas with up to N-H similar to 10(24) cm(-2), are the most convincing power source. The hydrogen column density estimated from the CO band is smaller than that inferred from X-ray observations. These results indicate that the region probed by the near-infrared CO absorption is in the vicinity of the nuclei and is located outside the X-ray emitting region. Furthermore, the covering factors of nearly unity required by the observed deep absorption profiles suggest that the probed region is close to the continuum source, which can be designated as the inner rim of the obscuring material around the
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The Astrophysical Journal 850(2) 193-193 2017年12月1日 査読有り筆頭著者Mid-infrared properties are reported of the west hot spot of the radio galaxy Pictor A with the Wide-field Infrared Survey Explorer (WISE). The mid-infrared counterpart to the hot spot, WISE J051926.26-454554.1, is listed in the AllWISE source catalog. The source was detected in all four of the WISE photometric bands. A comparison between the WISE and radio images reinforces the physical association of the WISE source to the hot spot. The WISE flux density of the source was carefully evaluated. A close investigation of the multi-wavelength synchrotron spectral energy distribution from the object reveals a mid-infrared excess at the wavelength of lambda = 22 mu m with a statistical significance of 4.8 sigma over the simple power-law extrapolation from the synchrotron radio spectrum. The excess is reinforced by single and double cutoff power-law modeling of the radio-to-optical spectral energy distribution. The synchrotron cutoff frequency of the main and excess components was evaluated as 7.1 x 10(14) Hz and 5.5 x 10(13) Hz, respectively. From the cutoff frequency, the magnetic field of the emission region was constrained as a function of the region size. In order to interpret the excess component, an electron population different from the main one dominating the observed radio spectrum is necessary. The excess emission is proposed to originate in a substructure within the hot spot, in which the magnetic field is a factor of a few stronger than that in the minimum-energy condition. The relation of the mid-infrared excess to the X-ray emission is briefly discussed.
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Publications of the Astronomical Society of Australia 34 2017年11月 査読有り<title>Abstract</title>A far-infrared observatory such as the <italic>SPace Infrared telescope for Cosmology and Astrophysics</italic>, with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last ~10 Gyr of the Universe (<italic>z</italic> = 1.5–2), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionised gas. We quantify the detectability of galaxy-scale massive molecular and ionised outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.
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Publications of the Astronomical Society of Australia 34 2017年11月 査読有り<title>Abstract</title>IR spectroscopy in the range 12–230 μm with the <italic>SPace IR telescope for Cosmology and Astrophysics (SPICA)</italic> will reveal the physical processes governing the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the <italic>James Webb Space Telescope</italic> and the upcoming Extremely Large Telescopes at shorter wavelengths and the Atacama Large Millimeter Array at longer wavelengths. The <italic>SPICA</italic>, with its 2.5-m telescope actively cooled to below 8 K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields, and gas-phase metallicities will be measured in dust-obscured galaxies and active galactic nuclei, sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. Active galactic nuclei and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. The <italic>SPICA</italic>’s large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of <italic>z</italic> ~ 6.
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The Astrophysical Journal 848(2) L12-L12 2017年10月16日 査読有りOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.
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Publications of the Korean Astronomical Society 32(1) 45-47 2017年3月31日 査読有り
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Publications of The Korean Astronomical Society 32(1) 185-187 2017年3月31日 査読有り筆頭著者
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Publications of The Korean Astronomical Society 32(1) 189-191 2017年3月31日 査読有り
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Publications of The Korean Astronomical Society 32(1) 209-211 2017年3月31日 査読有り
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Publications of The Korean Astronomical Society 32(1) 363-365 2017年3月31日 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68(6) 2016年12月Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far infrared wavelengths with Monitor of All-sky X-ray Image (MAXI) and the Japanese infrared observatory AKARI, respectively. One hundred of the X-ray sources listed in the second release of theMAXI all-sky X-ray source catalog are currently identified as non-blazar-type active galactic nuclei. These include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1 and 27 type-2 objects. The AKARI all-sky survey point source catalog was searched for their mid-and far-infrared counterparts at 9, 18, and 90 mu m. As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV) and infrared luminosities of these objects were investigated, together with their color information. Adopting the canonical photon index, Gamma = 1.9, of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness ratio between the 3-4 and 4-10 keV ranges derived with MAXI was roughly converted into the absorption column density. After the X-ray luminosity was corrected for absorption from the estimated column density, the well-known X-ray-to-infrared luminosity correlation was confirmed, at least in the Compton-thin regime. In contrast, NGC 1365, the only Compton-thick object in the MAXI catalog, was found to deviate from the correlation toward a significantly lower X-ray luminosity by nearly an order of magnitude. It was verified that the relation between the X-ray hardness below 10 keV and X-ray-to-infrared color acts as an effective tool to pick up Compton-thick objects. The difference in the infrared colors between the type-1 and type-2 Seyfert galaxies and its physical implication on the classification and unification of active galactic nuclei are briefly discussed.
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ASTROPHYSICAL JOURNAL 833(2) 2016年12月We conducted systematic observations of the H I Bra line (4.05 mu m) and the polycyclic aromatic hydrocarbon (PAH) feature (3.3 mu m) in 50 nearby (z < 0.3) ultraluminous infrared galaxies (ULIRGs) with AKARI. The Bra line is predicted to be the brightest among the H I lines under conditions of high dust extinction (A(V) > 15 mag). The Bra line traces ionizing photons from OB stars and so is used as an indicator of star formation on the assumption of the initial mass function. We detected the Br alpha line in 33 ULIRGs. The luminosity of the line (L-Br alpha) correlates well with that of the 3.3 mu m PAH emission (L-3.3). Thus we utilize L-3.3 as an indicator of star formation in fainter objects where the Bra line is undetected. The mean L-Br alpha/L-IR ratio in LINERs/Seyferts is significantly lower than that in H II galaxies. This difference is reconfirmed with the L-3.3/L-IR ratio in the larger sample (46 galaxies). Using the ratios, we estimate that the contribution of starburst in LINERs/Seyferts is similar to 67%, and active galactic nuclei contribute the remaining similar to 33%. However, comparing the number of ionizing photons, Q(Br alpha), derived from L-Br alpha with that, Q(IR), expected from the star formation rate required to explain L-IR, we find that the mean Q(Br alpha)/Q(IR) ratio is only (55.5 +/- 7.5)% even in H II galaxies, which are thought to be energized by pure starburst. This deficit of ionizing photons traced by the Bra line is significant even taking heavy dust extinction into consideration. We propose that dust within H II regions absorbs a significant fraction of ionizing photons.
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Publications of the Astronomical Society of Japan 68(SP1) S1 2016年4月21日<jats:title>Abstract</jats:title> <jats:p>Various transient phenomena on a timescale ranging from seconds to days appear at unexpected sky positions in X-rays. MAXI, Monitor of All-sky X-ray Image, on the International Space Station has been monitoring about 95% of the sky a day and has detected transient objects since 2009 August. Here, we describe quasi-real-time data processing systems of MAXI and a subsequent nova-alert system to find transient objects, and present the capabilities for the nova-alert system to detect transient events with excess fluxes from ≳80 mCrab in a single scan transit to ≳8 mCrab for 4 d, and to send prompt alert information to the world in less than 30 s after the onboard detection of a burst, making the best use of the International Space Station (ISS) real-time network. We also report on highlights of scientific results obtained with the system until the end of the first extended mission phase, 2015 March. Including 15 X-ray novae solely or independently discovered, we have reported on 177 transient phenomena, such as X-ray bursts, outbursts, and state transitions of X-ray binaries and X-ray flares from active stars and blazars, via the Astronomer's Telegram, and on 63 burst phenomena of other types via the Gamma-ray Coordinates Network. We summarize the results of these transient sources and phenomena focusing on the detections with the nova-alert system, and some new transients yet unpublished or requiring attention.</jats:p>
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68(2) 2016年4月We perform revised spectral calibrations for the AKARI near-infrared grism to correct quantitatively for the effect of the wavelength-dependent refractive index. The near-infrared grism covering the wavelength range of 2.5-5.0 mu m, with a spectral resolving power of 120 at 3.6 mu m, is found to be contaminated by second-order light at wavelengths longer than 4.9 mu m, which is especially serious for red objects. First, we present the wavelength calibration considering the refractive index of the grism as a function of the wavelength for the first time. We find that the previous solution is positively shifted by up to 0.01 mu m compared with the revised wavelengths at 2.5-5.0 mu m. In addition, we demonstrate that second-order contamination occurs even with a perfect order-sorting filter owing to the wavelength dependence of the refractive index. Secondly, the spectral responses of the system from the first-and second-order light are simultaneously obtained from two types of standard objects with different colors. The response from the second-order light suggests leakage of the order-sorting filter below 2.5 mu m. The relations between the output of the detector and the intensities of the first- and second-order light are formalized by a matrix equation that combines the two orders. The removal of the contaminating second-order light can be achieved by solving the matrix equation. The new calibration extends the available spectral coverage of the grism mode from 4.9 mu m up to 5.0 mu m. The revision can be used to study spectral features falling in these extended wavelengths, e. g., the carbon monoxide fundamental ro-vibrational absorption within nearby active galactic nuclei.
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Proceedings of SPIE - The International Society for Optical Engineering 9904 2016年SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane scientific instruments planned for new SPICA, and the Japanese instrument proposed and managed by a university consortium in Japan. SMI covers the wavelength range of 12 to 36 μm, using the following three spectroscopic channels with unprecedentedly high sensitivities: low-resolution spectroscopy (LRS; R = 50 - 120, 17 - 36 μm), mid-resolution spectroscopy (MRS; R = 1300 - 2300, 18 - 36 μm), and high-resolution spectroscopy (HRS; R = 28000, 12 - 18 μm). The key functions of these channels are high-speed dustband mapping with LRS, high-sensitivity multi-purpose spectral mapping with MRS, and high-resolution molecular-gas spectroscopy with HRS. This paper describes the technical concept and scientific capabilities of SMI.
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Proceedings of SPIE - The International Society for Optical Engineering 9904 2016年We present the new design of the cryogenic system of the next-generation infrared astronomy mission SPICA under the new framework. The new design employs the V-groove design for radiators, making the best use of the Planck heritage. The new design is based on the ESA-JAXA CDF study (NG-CryoIRTel, CDF-152(A)) with a 2 m telescope, and we modified the CDF design to accommodate the 2.5 m telescope to meet the science requirements of SPICA. The basic design concept of the SPICA cryogenic system is to cool the Science Instrument Assembly (SIA, which is the combination of the telescope and focal-plane instruments) below 8K by the combination of the radiative cooling system and mechanical cryocoolers without any cryogen.
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Publications of the Astronomical Society of Japan 67(4) 77-77 2015年8月1日 査読有りX-ray emission associated with the west lobe of the giant radio galaxy 3C 236 was investigated with the Suzaku observatory to evaluate the energetics in the lobe. After removing contamination from point-like X-ray sources detected with Chandra and subtracting the X-ray and non-X-ray backgrounds, the Suzaku spectrum from the lobe was reproduced by a power-law model with a photon index of $\\Gamma = 2.23-{-0.38-0.12}^{+0.44+0.14}$, where the first and second errors represent the statistical and systematic ones, respectively. Within the errors, the X-ray index was consistent with the radio synchrotron one, Γ< inf> R< /inf> = 1.74 ± 0.07, estimated in the 326-2695 MHz range. This agreement supports that the X-ray emission is attributed to the inverse-Compton radiation from the synchrotron electrons filling the lobe, where the cosmic microwave background photons are up-scattered. This result made 3C 236 the largest radio galaxy of which the lobe has ever been probed through the inverse-Compton X-ray photons. When the photon index was fixed at Γ< inf> R< /inf> , the X-ray flux density at 1 keV was measured as S< inf> X< /inf> = 12.3 ± 2.0 ± 1.9 nJy. A comparison of the X-ray flux to the radio one (S< inf> R< /inf> = 1.11 ± 0.02 Jy at 608.5 MHz) yields the energy densities of the electrons and magnetic field in the west lobe as $u-{\\rm e} = 3.9-{-0.7 -0.9}^{+0.6 +1.0} \\times 10^{-14}$ erg cm< sup> -3< /sup> and $u-{\\rm m} = 0.92-{-0.15 -0.35}^{+0.21 +0.52}\\times 10^{-14}$ erg cm< sup> -3< /sup> , respectively, indicating a mild electron dominance of $u-{\\rm e}/u-{\\rm m} = 4.2-{-1.3 -2.3}^{+1.6 +4.1}$. The latter corresponds to the magnetic field strength of $B = 0.48-{-0.04 -0.10}^{+0.05 +0.12}\\ \\mu$G. These are typical among the lobes of giant radio galaxies. A summary of the u< inf> e< /inf> -size relation for the inverse-Compton-detected radio galaxies implies that the west lobe of 3C 236 is still actively energized by its jet.
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Publications of the Astronomical Society of Japan 67(4) 2015年5月25日We investigate the position of the radio core in a blazar by multi-epoch astrometric observations at 43 GHz. Using the VLBI Exploration of Radio Astrometry (VERA), we have conducted four adjacent observations in 2011 February and another four in 2011 October, and succeeded in measuring the position of the radio core in the TeV blazar Mrk 501 relative to a distant compact quasar NRAO 512. During our observations, we find that (1) there is no positional change within ∼0.2 mas or ∼2.0 pc de-projected with ±1 σ error for the weighted-mean phase-referenced positions of the Mrk 501 core relative to NRAO 512 over four adjacent days, and (2) there is an indication of position change for the 3C 345 core relative to NRAO 512. By applying our results to the standard internal shock model for blazars, we constrain the bulk Lorenz factors of the ejecta.
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ASTROPHYSICAL JOURNAL 798(1) 27 2015年1月 査読有りThe archetypical very-high-energy gamma-ray blazar Mrk 421 was monitored for more than three years with the Gas Slit Camera on board Monitor of All Sky X-ray Image (MAXI), and its long-term X-ray variability was investigated. The MAXI light curve in the 3-10 keV range was transformed into the periodogram in the frequency range f = 1 x 10(-8)-2 x 10(-6) Hz. The artifacts on the periodogram, resulting from data gaps in the observed light curve, were extensively simulated for variations with a power-law-like power spectrum density (PSD). By comparing the observed and simulated periodograms, the PSD index was evaluated as alpha = 1.60 +/- 0.25. This index is smaller than that obtained in the higher-frequency range (f greater than or similar to 1 x 10(-5) Hz), namely, alpha = 2.14 +/- 0.06 in the 1998 ASCA observation of the object. The MAXI data impose a lower limit on the PSD break at f(b) = 5 x 10(-6) Hz, consistent with the break of f(b) = 9.5 x 10(-6) Hz suggested from the ASCA data. The low-frequency PSD index of Mrk 421 derived with MAXI falls well within the range of typical values among nearby Seyfert galaxies (alpha = 1-2). The physical implications from these results are briefly discussed.
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JOURNAL OF ASTROPHYSICS AND ASTRONOMY 35(3) 215-218 2014年9月 査読有りWe made simultaneous single-dish and VLBI observations of a gamma-ray narrow-line Seyfert 1 (NLS1) galaxy 1H 0323+342. We found significant flux variation at 8 GHz on a time scale of one month. The total flux density varied by 5.5% in 32 days, corresponding to a variability brightness temperature of 7.0 x 10(11) K. We also obtained brightness temperatures of greater than 5.2 x 10(10) K from the VLBI images. These high brightness temperatures suggest that the source has nonthermal processes in the central engine. The source structure could be modelled by two elliptical Gaussian components on the parsec scales. The flux of the central component decreases in the same way as the total flux density, showing that the short-term variability is mainly associated with this component.
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Astrophysical Journal 788(1) 2014年6月10日In this work, we investigate the dependence of the covering factor (CF) of active galactic nuclei (AGNs) on the mid-infrared (MIR) luminosity and the redshift. We constructed 12 and 22 μm luminosity functions (LFs) at 0.006 ≤z ≤ 0.3 using Wide-field Infrared Survey Explorer (WISE) data. Combining the WISE catalog with Sloan Digital Sky Survey (SDSS) spectroscopic data, we selected 223,982 galaxies at 12 μm and 25,721 galaxies at 22 μm for spectroscopic classification. We then identified 16,355 AGNs at 12 μm and 4683 AGNs at 22 μm by their optical emission lines and cataloged classifications in the SDSS. Following that, we estimated the CF as the fraction of Type 2 AGN in all AGNs whose MIR emissions are dominated by the active nucleus (not their host galaxies) based on their MIR colors. We found that the CF decreased with increasing MIR luminosity, regardless of the choice of Type 2 AGN classification criteria, and the CF did not change significantly with redshift for z ≤ 0.2. Furthermore, we carried out various tests to determine the influence of selection bias and confirmed that similar dependences exist, even when taking these uncertainties into account. The luminosity dependence of the CF can be explained by the receding torus model, but the "modified" receding torus model gives a slightly better fit, as suggested by Simpson. © 2014. The American Astronomical Society. All rights reserved..
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ASTROPHYSICAL JOURNAL 781(2) 75 2014年2月 査読有りWe made simultaneous single-dish and very long baseline interferometer (VLBI) observations of a narrow-line Seyfert 1 galaxy 1H 323+342, showing gamma-ray activity revealed by Fermi/Large Area Telescope observations. We found significant variation of the total flux density at 8 GHz on the timescale of one month by the single-dish monitoring. The total flux density varied by 5.5% in 32 days, which is comparable to the gamma-ray variability timescale, corresponding to the variability brightness temperature of 7.0 x 10(11) K. The source consists of central and southeastern components on the parsec (pc) scale. Only the flux of the central component decreased in the same way as the total flux density, indicating that the short-term radio variability, and probably the gamma-ray-emitting region, is associated with this component. From the VLBI observations, we obtained brightness temperatures of greater than (5.2 +/- 0.3) x 10(10) K and derived an equipartition Doppler factor of greater than 1.7, a variability Doppler factor of 2.2, and an 8 GHz radio power of 10(24.6) W Hz(-1). Combining them, we conclude that acceleration of radio jets and creation of high-energy particles are ongoing in the central engine and that the apparent very radio-loud feature of the source is due to the Doppler boosting effect, resulting in the intrinsic radio loudness being an order of magnitude smaller than the observed values. We also conclude that the pc-scale jet represents recurrent activity from the spectral fitting and the estimated kinematic age of pc- and kpc-scale extended components with different position angles.
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SPACE TELESCOPES AND INSTRUMENTATION 2014: OPTICAL, INFRARED, AND MILLIMETER WAVE 9143 2014年The contamination control for the next-generation space infrared observatory SPICA is presented. The optical performance of instruments on space observatories are often degraded by particulate and/or molecular contamination. Therefore, the contamination control has a potential to produce a significant risk, and it should be investigated in the risk mitigation phase of the SPICA development. The requirements from contamination-sensitive components onborad SPICA, the telescope assembly and focal plane instruments, are summarized. Possible contamination sources inside and outside the SPICA spacecraft were investigated. Based on impact on the SPICA system design, the following contamination sources were extensively studied through simulation and measurement; (1) outgassing from the payload module surrounding the telescope mirror and focal plane instruments, (2) contamination due to the thruster plume, and (3) environmental contamination during the integration, storage and verification phases. Although the outgas from the payload module and the thruster plume were estimated to produce only a negligible influence, the environmental contamination was suggested to affect significantly the telescope and focal plane instruments. Reasonable countermeasures to reduce the environmental contamination were proposed, some of which were confirmed to be actually effective.
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Publications of the Astronomical Society of Japan 65(4) 2013年8月25日 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 65(3) 2013年6月We report on the spectral evolution of a new X-ray transient, MAXI J0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera all-sky survey at (l, b) = (238 degrees.9, -25 degrees.2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXI J0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following similar to 70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 x 10(37) erg s(-1). This suggests a source distance of > 17 kpc.
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Publications of the Astronomical Society of Japan 65(2) 48-48 2013年4月25日 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(6) "119-1"-"119-10" 2012年12月 査読有りThe X-ray spectrum of the nearest ultraluminous X-ray source, M 33 X-8, obtained by Suzaku during 2010 January 11-13, was closely analyzed in order to examine its nature. It is, by far, the only data with the highest signal statistic in the 0.4-10 keV range. Despite being able to reproduce the X-ray spectrum, Comptonization of the disk photons failed to give a physically meaningful solution. A modified version of the multi-color disk model, in which the dependence of the disk temperature on the radius is described as r(-p), with p being a free parameter, can also approximate the spectrum. From this model, the innermost disk temperature and bolometric luminosity were obtained as T-in = 2.00(-0.05)(+0.06) keV and L-disk = 1.36 x 10(39)(cos i)(-1) erg s(-1), respectively, where i is the disk inclination. A small temperature gradient of p = 0.535(-0.005)(+0:004), together with the high disk temperature, is regarded as signatures of the slim accretion disk model, suggesting that M 33 X-8 was accreting at a high mass-accretion rate. With a correction factor for the slim-disk taken into account, the innermost disk radius, R-in = 81.9(-6.5)(+5.9)(cos i)(-0.5) km, corresponds to a black-hole mass of M similar to 10M(circle dot)(cosi)(-0.5). Accordingly, the bolometric disk luminosity is estimated to be about 80(cos i)(-0.5)% of the Eddington limit. A numerically calculated slim-disk spectrum was found to reach a similar result. Thus, the extremely super-Eddington luminosity is not required to explain the nature of M 33 X-8. This conclusion is utilized to argue for the existence of intermediate-mass black holes with M greater than or similar to 100 M-circle dot radiating at the sub/trans-Eddington luminosity, among ultraluminous X-ray sources with L-disk greater than or similar to 10(40) erg s(-1).
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ASTROPHYSICAL JOURNAL 759(2) 1-7 2012年11月 査読有りWe report on the very long baseline interferometry (VLBI) follow-up observations using the Japanese VLBI Network array at 22 GHz for the largest X-ray flare of TeV blazar Mrk 421 that occurred in 2010 mid-February. The total of five epochs of observations were performed at intervals of about 20 days between 2010 March 7 and May 31. No newborn component associated with the flare was seen directly in the total intensity images obtained by our multi-epoch VLBI observations. However, one jet component located at similar to 1 mas northwest from the core was able to be identified, and its proper motion can be measured as -1.66 +/- 0.46 mas yr(-1), which corresponds to an apparent velocity of -3.48 +/- 0.97c. Here, this negative velocity indicates that the jet component was apparently moving toward the core. As the most plausible explanation, we discuss that the apparent negative velocity was possibly caused by the ejection of a new component, which could not be resolved with our observations. In this case, the obtained Doppler factor of the new component is around 10-20, which is consistent with the ones typically estimated by model fittings of spectral energy distribution for this source.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(4) 2012年8月We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar, LS V +44 17/RX.10440.9+4431, and the discovery of an absorption dip structure in the pulse profile. An outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of transient activity of LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of a follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile, which was clearer in the lower-energy bands. The pulse-phase-averaged energy spectra in the 3-100 keV band could be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron K alpha emission line was also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column.
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りWe report a result of our Suzaku observations for two ultraluminous X-ray sources (ULX; X-1 and X-2) in IC 342 on 2010 August and 2011 March. We found a hint of hard X-ray photons (14-20 keV), and fitted the XIS and the PIN spectra simultaneously. As a result, the joint spectra can be explained by the power-law model for X-1 and the multi-color disk model for X-2. We briefly discuss the spectral states of the two ULXs comparing with those of Galactic black hole binaries.
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りSuzaku observations are reported of the three giant radio galaxies, 3C 35, 3C 326, and DA 240, with a projected linear size of greater than or similar to 1 Mpc. The low and stable instrumental background of the X-ray Imaging Spectrometer onboard Suzaku allows a significant detection of inverse Compton X-ray emission from the lobes of these giant radio galaxies. As a result, the electron and magnetic energy densities in the lobes were measured. Based on the measurements, the late phase in the evolution of the energetics associated with jets from active galactic nuclei was investigated. It is found that the lobes of giant radio galaxies tend to reside in a near equipartition condition between electrons and magnetic field, despite the fact that smaller sources with sizes of about 100 kpc exhibit a particle dominance by a typical factor of 10 in energy density. In addition, the energy densities in the giant lobes are measured to be smaller by an order of magnitude as compared to the extrapolation of the size to energy density correlation found for smaller radio galaxies. These results indicate that typical radio galaxies experience a significant reduction in their jet power, as their jets evolve in size from 100 kpc to 1 Mpc.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(SPEC. ISSUE 3) S713-S716 2011年11月 査読有りWe present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of 3 x 10(-9) erg cm(-2)s(-1) in 2-20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3 x 10(32) erg s(-1), indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log L-X/L-bol = -0.1(-0.3)(+0.2); i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S947-S955 2011年11月 査読有りA careful analysis of the Suzaku data of the giant radio galaxy DA 240, of which the size is 1.48 Mpc, revealed diffuse X-ray emission associated with its east lobe. The diffuse X-ray spectrum was described with a simple power-law model with a photon index of Gamma = 1.92(-0.17-0.06)(+0.13+0.04) where the first and second errors represent the statistical and systematic ones. The agreement with the synchrotron radio photon index, Gamma(R) = 1.95 +/- 0.01 in 326-608.5 MHz, ensures that any excess X-ray emission is attributed to inverse Compton emission from the synchrotron-radiating electrons, boosting up the cosmic microwave background photons. From the X-ray flux density, 51.5 +/- 3.91(-5.4)(+6.2) nJy at 1 keV, derived with the photon index fixed at Gamma(R), in comparison with the synchrotron radio intensity of 10.30 +/- 0.12 Jy at 326 MHz, the magnetic and electron energy densities were estimated as u(m) = (3.0 +/- 0.2 +/- 0.4) x 10(-14)erg cm(-3) and u(e) =(34(-0.2-0.4)(+0.3+0.5)) x 10(-14)erg cm(-3) integrated over the electron Lorentz factor of 10(3)-10(5), respectively. Thus, the east lobe is found to reside in an equipartition condition between the electrons and magnetic field parametrized as u(e)/u(m) = 1.1(-0.1-0.2)(+0.2+0.4). The east lobe of DA 240 is indicated to exhibit the lowest value of tie, among all of the X-ray detected lobes of radio galaxies. A comparison of the energetics in the giant radio galaxies with a size of 1 Mpc to those in the smaller objects suggests a possibility that radio galaxies lose their jet power as they evolve from similar to 100 kpc to similar to 1 Mpc.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S1035-S1040 2011年11月The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB 090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be r(0) = (4.3 +/- 0.9) x 10(9) Y'(-3/2) cm, the Lorentz factor of the plasma is Gamma = (110 +/- 10) Y'(1/4), where Y' is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This r(0) is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.
MISC
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VizieR On-line Data Catalog 2023年10月
講演・口頭発表等
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The 32nd Texas Symposium on Relativistic Astrophysics 2023年12月15日
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2023年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2021年4月 - 2025年3月
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日本学術振興会 科学研究費助成事業 2010年 - 2012年
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日本学術振興会 科学研究費助成事業 2008年 - 2011年
